1. Field of the Invention
The present invention relates to a zoom flash which adjusts the flash illumination angle in accordance with a variation of the focal length of a photographing lens, and further relates to a flash photography system, wherein the amount of light of the main flash discharge is controlled in accordance with photometric readings obtained at a pre-flash emission.
2. Description of the Related Art
Various types of cameras with which a flash photography is possible in which one or more flash devices are actuated to emit a pre-flash emission (preliminary flash emission) to determine the reflectivity of the subject (an object) before the main flash discharges wherein the amount of light of the main flash discharge is controlled in accordance with photometric readings obtained at the pre-flash emission are known in the art.
However, in the case of using a zoom flash (a zoom flash device) which adjusts the flash illumination angle in accordance with a variation of the focal length of the photographing lens, correct photometric readings cannot be obtained at the pre-flash emission when the light amount of the pre-flash emission is constant because the intensity of the pre-flash emission varies in accordance with zooming of the zoom flash. Therefore, it is sometimes the case that correct exposure is not achieved for the main object in flash photography.
An object of the present invention is to provide a flash photography system in which correct exposure can be attained to the main subject even if a plurality of zoom flashes with different illumination angles are used or even if a plurality of flash devices with different guide numbers are used.
Another object of the present invention is to provide a zoom flash that is used in such a flash photography system.
To achieve the objects mentioned above, according to an aspect of the present invention, a zoom flash is provided, including a light emitter, a zoom driver which moves the light emitter along an axis to vary an illumination angle, a detecting device which detects a zoom position of the light emitter, a calculation device which calculates a pre-flash emission level according to the detected zoom position so that illuminance on an object at a predetermined distance is substantially constant regardless of a variation of the illumination angle, and a control device which activates the light emitter to emit a preliminary flash emission, before a main flash emission, by supplying a voltage corresponding to the pre-flash emission level for the light emitter.
Preferably, the calculation device calculates the pre-flash emission level so that an effective guide number is substantially constant regardless of the variation of the illumination angle.
In an embodiment, the zoom flash further includes a memory in which a maximum guide number that varies in accordance with the zoom position, a reference guide number predetermined as a constant, and a reference flash emission level predetermined as a correction constant are stored; wherein the maximum guide number, the reference guide number, and the reference flash emission level are stored in the memory, and wherein the calculation device calculates a pre-flash emission level using the following equation:
Vfp=Vaxc3x97(Gnos/Gno(zoom))2
wherein xe2x80x9cVfpxe2x80x9d represents the pre-flash emission level; xe2x80x9cVaxe2x80x9d represents the reference flash emission level; xe2x80x9cGnosxe2x80x9d represents the reference guide number; and xe2x80x9cGno(zoom)xe2x80x9d represents the maximum guide number corresponding to the detected zoom position.
Preferably, the zoom flash further includes a terminal connector via which the zoom flash can be electrically connected to a camera body. The zoom driver moves the light emitter in accordance with a focal length of a photographing lens of the camera body in a case where the zoom flash is electrically connected to the camera body.
In an embodiment, the control device controls the light emitter perform a pre-flash emission in a flat emission mode.
According to another aspect of the present invention, a flash photography system is provided, having a camera body and at least one zoom flash, the zoom flash being activated to emit a preliminary flash emission before a main flash emission. The zoom flash includes a light emitter, a zoom driver which moves the light emitter along an axis to vary an illumination angle, and a detecting device which detects a zoom position of the light emitter. Either the camera body or the zoom flash includes a calculation device which calculates a pre-flash emission level according to the detected zoom position so that an illuminance on an object at a predetermined distance is substantially constant regardless of a variation of the illumination angle, and a control device which activates the light emitter to emit a preliminary flash emission by supplying a voltage corresponding to the pre-flash emission level for the light emitter before a main flash emission.
Preferably, the calculation device calculates the pre-flash emission level so that an effective guide number is substantially constant regardless of the variation of the illumination angle.
In an embodiment, the zoom flash further includes a memory in which a maximum guide number that varies in accordance with the zoom position, a reference guide number predetermined as a constant, and a reference flash emission level predetermined as a correction constant are stored; wherein the maximum guide number, the reference guide number, and the reference flash emission level are stored in the memory, and wherein the calculation device calculates a pre-flash emission level using the following equation:
Vfp=Vaxc3x97(Gnos/Gno(zoom))2
wherein xe2x80x9cVfpxe2x80x9d represents the pre-flash emission level; xe2x80x9cVaxe2x80x9d represents the reference flash emission level; xe2x80x9cGnosxe2x80x9d represents the reference guide number; and xe2x80x9cGno(zoom)xe2x80x9d represents the maximum guide number corresponding to the detected zoom position.
Preferably, the flash photography system further includes a terminal connector via which the zoom flash can be electrically connected to a camera body. The zoom driver moves the light emitter in accordance with a focal length of a photographing lens of the camera body in a case where the zoom flash is electrically connected to the camera body.
In an embodiment, the control device controls the light emitter perform a pre-flash emission in a flat emission mode.
The present disclosure relates to subject matter contained in Japanese Patent Application No.2000-284413 (filed on Sep. 19, 2000) and No.2001-34580 (filed on Feb. 9, 2001), which are expressly incorporated herein by reference in their entireties.